The present invention is directed to antennae for use in high frequency communications systems. Specifically, the present invention relates to a polarization rotator for use in high frequency antennae which allows the polarization of signals to be changed as they pass through a waveguide.
Waveguide systems including rotator elements for changing the polarization of a radio signal are well known in the art. Typically, a conventional waveguide system such as that disclosed in U.S. Pat. No. 6,404,298 to S. Rohr et al. includes at least 3 separate rotators located between two waveguides. Each individual rotator has a central passage hole with a cross section corresponding to the open cross section of the waveguides. Each rotator is rotated with respect to the adjacent rotators and the waveguides in order to accomplish the polarization change from the first waveguide to the second.
In high frequency communications systems, it is often necessary to change the polarization of an incoming radio signal prior to the processing of the signal. In particular, waveguide systems used in high frequency radio communications systems include at least one input waveguide and one output waveguide with a series of rotator elements between them designed to change the polarization of the signal.
Conventional high frequency antennas required waveguide systems with a number of rotator elements between the input and output waveguide to accomplish the polarization change.
Specifically, to change the polarization by ninety-degrees each rotator element was rotated by a small amount with respect to adjacent rotator elements, so that the cumulative change across all of the rotator elements between the waveguides would be the desired ninety-degree polarization change.
However, introducing a large number of rotators between the waveguides has a number of problems. The interfaces between adjacent rotators have to be as tightly sealed as possible because poor contact between the rotator disks can significantly reduce signal flow, thereby reducing the usefulness and efficiency of the antenna. In addition, the tight linkage between the adjacent rotator elements requires high precision manufacture, installation, and assembly, which greatly increases the labor time and cost.
Furthermore, additional disks enlarge the overall size of the waveguide system of the antenna. Therefore, manufacturers and service providers have tried to keep the number of disks as low as possible to mitigate these problems.
Based on conventional waveguide systems three rotator disks have been the minimum number possible that would allow a polarization change and be cost effective to manufacture and maintain. Having three rotator disks, means that the conventional waveguide system will have four interfaces, one between the first waveguide and a rotator, two interfaces between the middle rotator and the rotators adjacent to it, and another interface between the second waveguide and the rotator adjacent to it. Furthermore, this conventional waveguide system requires multiple steps to accomplish the polarization change.
What is needed is an antenna feed capable of accomplishing the requisite polarization change with a minimum of effort in a minimum number of steps, with the fewest number of interfaces and parts that can be manufactured cost-effectively.
In view of the foregoing, the present invention provides an integrated antenna feed for sending and receiving high frequency radio signals. In one embodiment, the antenna feed includes a first waveguide having a cavity and a cavity wall and a second waveguide with a first cavity wall and a second cavity wall perpendicular to the first cavity wall. The second waveguide is rotatable around an axis to align either the first cavity wall or the second cavity wall with the cavity wall of the first waveguide. A rotator between the waveguides has a first portion adjacent to the first waveguide and a second portion adjacent to the second waveguide. Each portion has an opening through which radio signals can pass.
The first and second cavities of the second waveguide respectively correspond to first and second polarizations of the antenna, and these polarization are orthogonal to each other.
In an embodiment, the cavity of the first waveguide and the cavity of the second waveguide have a substantially rectangular cross sections, and the width of the second cavity wall of the second waveguide is greater than the width of the first cavity wall of the second waveguide.
In one embodiment, the width and height of the rotator openings at the first and second portions of the rotator are the same. In addition, the opening of the first portion is rotated by an angle gamma with respect to the opening of the second portion. In another embodiment, the thickness of each of the first and second portions of the rotator is equal to half the thickness of the rotator.
In the first configuration corresponding to a first polarization, the rotator is disposed at an acute angle alpha with respect to the cavity of the first waveguide.
In the second configuration corresponding to a second polarization, the second waveguide is rotated such that said second cavity wall is aligned with the cavity wall of the first waveguide, and the rotator is rotated by an acute angle beta with respect to the first waveguide.